This application claims priority to European Application Serial Number 00 870 148.4, filed Jun. 30, 2000, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a damping device of xe2x80x9csqueeze filmxe2x80x9d type which acts as a pressurized-oil damper, integrated in a rolling bearing, which is intended in particular to be used in civil aeronautics.
Specifically, the invention relates to the rolling bearing using the damping device.
2. Description of Related Art
A rolling bearing such as, for example, in an aircraft engine, serves as a link between one or more inner mobile members, preferably having a revolution symmetry and rotating about an axis, and an outer structure. The outer structure may itself be either fixed or mobile. This structure also has a revolution symmetry relative to the rotational axis of the mobile member(s). It may be, for example, in the shape of a cone.
The rolling bearing consists substantially of balls or rollers which move on tracks that are securely fastened or made with races, preferably an inner race and an outer race.
When working, forces are transmitted from the mobile member to the outer structure, in particular via the outer rolling race, which is directly in contact with the outer structure.
In order to damp the effect of these forces, it is known to confine a film of oil between the outer rolling race, which works by friction, and the outer structural component. This film of oil is commonly known as a xe2x80x9csqueeze filmxe2x80x9d.
The oil present at the race/outer structure contact surface is oil under pressure, which acts as a damper.
Most of the known xe2x80x9csqueeze filmsxe2x80x9d annulus are made leakproof by means of seals in the form of segments of xe2x80x9cpistonxe2x80x9d type. These seals are placed in two annular grooves machined in the race at its surface of contact with the outer structure. The film of oil is consequently more particularly confined in the space delimited by these two annular grooves.
The main problem lies in sealing such a device.
Document U.S. Pat. No. 4,175,803, in particular, describes the xe2x80x9csqueeze filmxe2x80x9d technique constituting a pressurized-oil damper, used particularly in engines of gas turbine type.
In these engines, two rolling bearings are used to maintain in a fixed structure, at its ends, the shaft bearing the vanes of the compressor and of the low-pressure turbine.
Similarly, two other rolling bearings are used to maintain in rotation, about the abovementioned shaft, the shaft bearing the vanes of the compressor and the vanes of the high-pressure turbine. One of the bearings bears on the abovementioned shaft, and the other bears on the fixed structure.
These four rolling bearings are examples of the field of application of the present invention.
The bearings are subjected to vibrations brought about by certain imbalances. During these vibrations, the hydraulic damping film (known as the xe2x80x9csqueeze filmxe2x80x9d) is xe2x80x9ccrushedxe2x80x9d at a point of the annular space which exists between the outer race and the outer structure surrounding this race.
The vibrations drive this xe2x80x9ccrush pointxe2x80x9d in an orbital (precessional) motion along the annular space.
The presence of oil maintained under pressure in the annular space, by means of the orbital motion, has the effect of creating a damping of the vibration.
In order to produce a sufficient and stable damping, it is desirable to maintain the xe2x80x9csqueeze filmxe2x80x9d annulus by means of a sealing device.
Most of the xe2x80x9csqueeze filmsxe2x80x9d proposed comprise seals of the same type as the piston segments of motor vehicle engines and they act at least partially by a radial pressure, such as, for example, in document FR-A-2 517 772.
This type of seal has various drawbacks. Dynamic seals of piston-segment type must be machined with great precision. They are thus expensive. Furthermore, they are intricate to mount. Finally, they have an uncalibrated oil leakage and thus their damping is not always fully controlled.
Document U.S. Pat. No. 4,440,456 describes a damping device of squeeze-film type for a rolling bearing.
In order to ensure sealing between the squeeze film and the rolling bearing, said bearing is provided with two seals of xe2x80x9cO-ringxe2x80x9d type (of circular cross section) each arranged in a groove.
The sealing is ensured by crushing said seal between the base of said groove and the side surface.
Documents U.S. Pat. No. 3,652,139, U.S. Pat. No. 3,756,672, U.S. Pat. No. 4,337,983 and U.S. Pat. No. 5,058,452 all describe damping devices of squeeze-film type in which seals of substantially circular shape (O-ring) arranged in grooves are provided, which ensure the sealing.
In each case, the sealing is ensured by crushing said seal between the base of said groove and the contact surface of the associated component. These are seals of elastomeric type which consequently have a limited lifetime, in particular in the case of applications used according to the present invention, that is to say as oil dampers for aircraft engines.
The present invention aims to provide a solution for the sealing of xe2x80x9csqueeze filmsxe2x80x9d dampers which does not have the drawbacks of the prior art.
The present invention aims more particularly to produce excellent sealing while at the same time having good reproducibility. The reason for this is that the oil leakage may thus be calibrated.
The present invention aims also to make possible the use of seals of moderate cost, in particular of seals which are almost standard seals and are substantially commercially available.
In particular, the present invention aims to provide an advantageous solution for rolling bearings, with or without a thrust bearing, used in civil aeronautic engines.
The present invention relates to a bearing for maintaining an inner mobile structural component with revolution symmetry, rotating inside an outer structural component, which is itself fixed or mobile, said bearing comprising a set of balls and at least one joining member which provides the mechanical contact between said balls and said outer structural component, said bearing also comprising a pressurized-oil damper known as a xe2x80x9csqueeze filmxe2x80x9d damper, arranged at the annular contact surface between said joining member and the outer structural component, said bearing comprising at least two annular elastic seals, each arranged in a groove, at the edges of said annular contact surface, wherein the annular elastic seals are U-shaped lip seals, the hollow space of which is directed towards the xe2x80x9csqueeze filmxe2x80x9d, or E-type seals, the hollow spaces of which are directed towards the xe2x80x9csqueeze filmxe2x80x9d. The leakproofing for each seal is ensured by the contact between said seal and the two parallel side surfaces of said groove, referred to as sealing side contact surfaces, such that the seal exerts axial pressure forces on said parallel side surfaces during the rotation of the bearing.
This mean ensures the leakproofing of the xe2x80x9csqueeze filmxe2x80x9d damper at the seal, substantially along its contact surface.
Advantageously, the annular elastic seals are U-shaped lip seals or E-type seals, the hollow space(s) of which is (are) directed towards the xe2x80x9csqueeze filmxe2x80x9d, so that the oil pressure gives rise to an axial pressure on the wings of the seals, which acts to promote the sealing.
Preferably, the U-shaped lip seals are polymeric seals, for example polyimide seals, comprising a spring member inside the xe2x80x9cUxe2x80x9d.
Preferably, the E-type seals are metallic seals.
Furthermore, according to the configuration used, the outside diameter of one of the two annular seals is not more than the inside diameter of the other annular seal.
According to one preferred embodiment, the two grooves are arranged asymmetrically on either side of said annular contact surface, one of the sealing side contact surfaces with said seal belonging to the outer structural component and the other sealing side contact surface with said seal belonging to said joining member.
According to one particularly advantageous embodiment of the present invention, the joining member has a first annular flange and the outer structural component has a second annular flange, the placing in contact of the outer structural component and the joining member cooperatively ensuring the formation of the groove in which the annular seal is arranged and compressed.
According to another embodiment of the present invention, said joining member consists of an outer rolling race.
According to another embodiment of the invention, said joining member consists of an outer rolling race and an intermediate race, said first annular flanges intended to form the grooves being located on said intermediate race.
The invention also relates to a joining member of a bearing for maintaining an inner mobile structural component with revolution symmetry, rotating inside an outer structural component, which is itself fixed or mobile, said bearing comprising a set of balls, said joining member ensuring the mechanical contact between said balls and said outer structural component, said bearing further comprising a pressurized-oil damper known as a xe2x80x9csqueeze filmxe2x80x9d damper, arranged at the annular contact surface between said joining member and the outer structural component; said joining member comprising at least two first annular flanges which cooperate with two second annular flanges machined in the structural component, during the placing in contact of said outer structural component and said joining member, to form at least two grooves, arranged at the edges of the annular contact surface between the joining member and the outer structural component, asymmetrically on either side of said annular contact surface, each groove resulting from placing a first flange opposite a second flange, at least two annular elastic seals being arranged in said grooves, the annular elastic seals being U-shaped lip seals, the hollow space of which is directed towards the xe2x80x9csqueeze filmxe2x80x9d, or E-type seals, the hollow spaces of which are directed towards the xe2x80x9csqueeze filmxe2x80x9d. The leakproofing for each seal is ensured by the contact between said seal and the two parallel side surfaces of said groove, so that the seal exerts axial pressure forces on said parallel side surfaces during the rotation of the bearing.
According to a first preferred embodiment, the joining member consists of an outer rolling race.
According to a second preferred embodiment, the joining member consists of an outer rolling race and an intermediate race, said first flanges intended to form the grooves being located on said intermediate race.